This invention relates to liquid crystal compositions for display elements, and more particularly it relates to liquid crystal compositions suitable for liquid crystal display elements according to multiplexing mode.
Recently, liquid crystal display apparatuses have been employed in various fields, and above all, in apparatuses needing a large number of informations, e.g. electronic calculators, matrix displays, etc., multiplexing mode according to voltage-leveling method, or the like has often been employed beside static drive mode. In the case of electronic calculators or the like, particularly a low voltage drive of 3 V drive which can be used in series connection of two cells, has been employed. This low voltage drive mode is characterized in that it is possible to keep the cell life over 500 to 2,000 hours by combining the above mode with C-MOSIC, without needing any voltage-elevating circuit. However, when the multiplexing mode is employed, a factor margin (M) which has never been raised as a problem in the case of the above static drive mode, has occurred as an important electroptical characteristic. The margin M is defined by the following equation: ##EQU1## wherein V.sub.10 represents a voltage at which the percentage transmission at the selected point at 0.degree. C. is 10% and V.sub.90 represents a voltage at which the percentage transmission at the non-selected point at 40.degree. C. is 90%. It is known that materials having a higher value of such margin M are suitable to the above multiplex.
Further, it has been experimentally known that as combinations of liquid crystal compounds which make the margin M higher, those of nematic liquid crystal compounds having a positive dielectric anisotropy (N.sub.p) with nematic liquid crystal compounds having a negative dielectric anisotropy (N.sub.n) show preferable results. Furthermore it has also been experimentally confirmed that the larger the proportion of the N.sub.n component in the compositions, the higher the margin M. On the other hand, the larger the proportion of the N.sub.n component, naturally the smaller the positive dielectric anisotropy .DELTA..epsilon. of the compositions. As a result the aimed low voltage drive is impossible.
One of other factors influencing the margin M is the temperature dependence of specific voltage values. In order to increase the margin M, it is necessary to make the temperature dependence of specific voltage values as small as possible. Further, in order that the low voltage drive is possible even in higher proportions of N.sub.n component in the compositions, it is necessary that the .DELTA..epsilon. of the N.sub.p component in the compositions be large; and in order to reduce the temperature dependence of specific voltage values, it is necessary to reduce the viscosity of the liquid crystal compositions. Thus the present inventors have made strenuous studies on liquid crystal compositions for multiplexing which can satisfy the above-mentioned various conditions. The object of the present invention is to provide such liquid crystal compositions for multiplexing.